1. Technical Field
The present invention relates to a device for suspension of a cab on a vehicle frame. The invention is intended in particular for construction machinery and contractor's machinery, the cab suspensions of which are subjected to relatively great stresses.
2. Background Art
Construction machinery/contractor's machinery such as, for example, wheel loaders and dumpers place considerable demands on the cab suspension construction. In order to make the working environment of the driver comfortable, the suspension must be capable of reducing/eliminating the relatively powerful vibrations and shocks which are otherwise transmitted from the vehicle frame to the cab. Moreover, for reasons of safety, the suspension must be sufficiently strong to retain the cab on the frame even if the vehicle should overturn. In this context, reference is frequently made to ROPS protection, where ROPS stands for Roll Over Protection Structure.
Conventionally, rubber has been included in the suspension construction in order to reduce the transmission of vibrations from frame to cab. In a traditional construction, the cab rests on a vibration element, usually taking the form of a “rubber collar” which is adapted for a through-type connecting means such as, for example, a bolt which connects the cab to the vehicle frame. The element of the suspension which serves for taking up load is usually arranged on the bolt under the vehicle frame. An example of a construction of this type is disclosed, for example, in U.S. Pat. No. 5,064,242. A disadvantage of this type of construction is that “rubber collars” do not meet current high requirements for vibration insulation/vibration damping.
In order to improve vibration-related characteristics, the utilization of what is known as “viscous mounts” or “hydro mounts” has become increasingly more common in suspension devices in recent years. Such vibration elements usually contain a viscous liquid, for example oil, which is used in order to reduce transmission of shocks and vibrations. A number of different alternatives have been proposed in functional solutions with the aim of combining the strength characteristics and vibration-damping characteristics of such suspension devices. An example is provided in EP 669484.
In most cases, the vibration-related and shock-related prevention characteristics are entirely adequate as far as elements of the “viscous mount” type are concerned, but the general problem is that strength characteristics are often limited. A known solution is to construct the vibration-damping element so that it meets prescribed strength requirements. The problem is then that the strength requirement has to be established once and for all because this requirement has a major influence on the manufacturing process. It is then difficult to adapt the construction to new circumstances. Another disadvantage of this solution is that the elements are relatively expensive.
Another solution is to make new attachment points and to mount one or more extra fastenings between the vehicle frame and the cab, parallel to (in front of, behind or at the side of) the vibration-damping element, in order to meet the strength requirements. The problem of this type of functional solution is that it requires considerable space and additional work for mounting and demounting, especially when the new attachment points require portions of the cab and/or the vehicle frame to be reinforced.